An ecosystem is a dynamic complex, that involves interactions between biotic and abiotic components. Ecosystem functioning involves several processes, including production, consumption and transfer of energy and material to higher trophic levels, organic matter decomposition, and nutrient regeneration.
Benthic organisms (macrofauna, meiofauna, and microorganisms), offer an ideal model tool to explore the relationships between biodiversity and ecosystem functioning, given their close relationship with the substrate or sediment.
Biodiversity and ecosystem functioning can change in response to different environmental factors. Therefore, studying biodiversity and functioning in different ecosystem settings and/or across environmental gradients can provide an indication of how ecosystems will respond to anthropogenic changes in environmental variables. During the Mirabilis2 expedition, researchers will use this approach to provide baseline information about pelagic and benthic biodiversity and functioning of the Cabo Verde bathyal and abyssal ecosystems.
Results from this expedition will be compared with the results that will be obtained at the end of the year during the BR_10 expedition to iAtlantic study area 10: Santos Basin in Brazil. This will be the first assessment of how climate-mediated changes in specific environmental variables may influence pelagic and benthic ecosystems in the Atlantic Ocean in the future.
Changes in POC
Particulate Organic Carbon (POC) export is a key energy source that sustains deep-sea communities, particularly the benthic organisms that strongly depends of the quantity and quality of organic matter that reaches the seafloor. In future climate change scenarios, the POC quantity and quality reaching these benthic communities is predicted to decline, in combination with warmer seafloor temperatures.
During iMirabilis2, we will study how altered POC fluxes and increased seafloor temperatures influence the functioning of deep-sea benthic ecosystems in eutrophic water masses. Sediment samples will be taken from the Cabo Verde slope at < 1000m depth by multicore and box-core deployments. These sediments will be incubated onboard under different treatments: only decreased POC influx quality, only increased seafloor temperatures, or both to study potentially synergistic effects. Ecosystem functioning under these different treatments are studied by measuring sediment respiration rates and assessing food-web cycling using stable isotope analysis. The results are compared to incubations with present-day temperature and ‘fresh’ POC influx.
Changes in nutrient flux
During iMirabilis2, in situ experiments will be run on the Cabo Verde abyssal plain, using a baited camera lander, a baited trap, and a respirometer lander. We will assess the benthic and pelagic biodiversity in the area, and test how benthic ecosystems are functioning naturally in an oligotrophic environment.
Baited camera deployments and baited trap experiments will be undertaken to catalogue abyssal scavenger fauna, their abundance and scavenging rates with trap-caught specimens providing voucher specimens to identify the fauna observed in camera footage.
Benthic respirometer experiments will be run in the westernmost abyssal region as well, using lander deployments of 48 hrs in order to measure seafloor respiration (O2 consumption, CO2 production), nutrient fluxes, and C flow through the benthic food web in each benthic incubation chamber. Carbon flow through the benthic food web will be quantified from isotopically labelled algal and bicarbonate tracers that will be injected into the benthic chambers at the beginning of the experiment. After the experiment, sediment and faunal samples will be processed in the lab to quantify the C incorporation into bacterial and faunal groups.
Nekton will also be sampled using bongo nets at random opportunistic locations to collect fauna for isotope signatures to elucidate pelagic trophic structure.